Method and apparatus for recording and reproducing sound



C. D. LINDRIDGE METHOD AND APPARATUS FOR RECORDING AND BEPRODUCING SOUND July 3, 1928. 1,675,894

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C. D. LINDRIDGE METHOD AND APPARATUS FOR RECORDING AND REPRODUCING SOUND Filed June 20, 1924 5 Sheet's5heet 3 Range covered by requmr method of ganqe covered by Recording .2 Reproducing speech inversion uam CONTROL by Wm] July 3, 1928.

C. D. LINDRIDGE METHOD AND APPARATUS FOR RECORDING AND REPRODUCING SOUND 5 Sheets-Sheet Filed June 20, 1924 1 AEU P SPEECH INVERTER July 3, 1928. 1,675,894

C. D. LINDRIDGE METHOD AND APPARATUS FOR RECORDING AND REPRQDUCING SOUND Filed June 20, 1924 5 Sheets-Sheet 5 SIEECH SPEECH INPUT OUDUD Patented July 3, 1928.

1 UNITED STATES I 1,675,894 PATENT OFFICE.

CHARLES D. LINERIDGE, 0F MONTCLAIR, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

METHOD AND APPARATUS FOR RECORDING AND REPRODUCING SOUND. A

Application filed Juneau, 1924. Serial no. 721,360.

This invention relates\to the art of transmitting, recording .and reproducing speech, music and other sounds or waves, and (particularly to photographically recor mg sound on a film and reproducing sound therefrom.

It has been found that when speech is recorded on a moving picture film by exposing the film to light, the intensity of which is varied in accordance with the speech, and is thereafter reproduced, the speech repro duced from the record is often distorted. The record on. the film consists of a series of relatively opaque areas separated by relatively transparent areas. The sounds oflow frequency produce relatively long areas upon which are superposed comparatively short areas corresponding to the high frequency sounds. The contrast between successive transparent and opaque areas corresponding to the high frequency sounds, 1n general, is reduced by the masking or obliterating effect of the background formed by the record of the low frequency waves, the contrast being especially poor in the opaque areas of the low frequency record. The reproduced high frequency sounds conseuently have a smaller amplitude than they s ould relatively to the low frequency sounds, and the reproduced speech 1s distorted.

The distribution of energy in the frequency spectrum of ordinary speech is such that a very large proportion of the energy lies in the low frequency ran 'e or fundamental frequencies, the hig frequency sounds, or harmonics, being relatively weak and producing only a feeble record in comparison to the low frequency sounds. The high frequency record is. accordinglvvery susceptible to' the masking eflect of the low frequency record. 7

According to another well known method, speech waves are recorded on a moving picture film as variations in the width of a record of constant transparency or opacity. This method, as practised, has the disadvantage of 'requirin large space for the record on the film. he average amplitude of the high frequency waves in speech is so much smaller than that of the low frequency waves that when the high frequency waves produce a record of smallest practicable width, the low frequency waves spread over an undesirable width of the film. The accuracy of reproduction of the low frequency sounds is not improved in proportion to the space occupied by the record and an appreciable portion of the space utilized by the low frequency waves may be considered uneconomical, especially when the rounds are recorded on a moving picture film where as large aspace as possible should be reserved for pictures.

In addition to the above described diflisulties and objections, it is found that varione parts of the a paratus usually employed of the wave components; to more efliectively utilize the space occupied by the record on i a photograph film, such as a moving picture film; to automatically produce a secondary record for a primary record and to readjust different portions of the record; to efiiciently transmit sound by means of light rays; and generally to provide simple and reliable methods and apparatus of the kind referred to.

In accordance with one aspect of the present invention, speech, music and other sounds or waves are recorded on a photographic film, or other element, 'by separately transmitting over different paths components of the waves within different freqeuncy ranges. The components are recorded and photo-electrically reproduced separately or together and transmitted to responsive apparatus, for example a telephone receiver. During these opera- .tions the quality of the reproduced waves may be controlled as desired y changing the relative amplitudes, frequencies or other characteristics of the waves in the different ranges. I

According to another feature of the im vention, waves to be recorded are transmitted to a modulator wherein the modulate a car rier wave and undergo a fi' equency change. Unmodulated components of modulatin and carrier wave frequency are suppressed; and modulated components are recorded on a photographic film or other element. Upon reproduction the modulated waves are demodulated. When speech or similar sounds are to be recorded on a narrow section of film, waves in only the lower portion of the frequency spectrum of the modulated waves, or waves principally of inverted frequency, are recorded in such a manner that they can be satisfactorily reproduced. The record of the modulated waves may be supplemented by a separate record of the lower frequency component waves.

When different wave components are separately recorded on a film the space allotted for the record of the high frequency components may be of the same width as, but 1s preferably of greater width than that of the low frequency components. When relativel high and low frequencies are to be recorde a record of the low frequencies may be made on the film as variations in the transparency of a strip of uniform width and a record of the high frequencies may be made as variations in the -width of a strip of uniform transparency or opacity. By making separate records in different colors and utilizing color selection in reproducing the waves, the records may be superposed on each otherwithout causing interference of the waves.

Secondary or master records are automatically made by reproducing waves from one or more primary records and recording the reproduced waves on the secondary recordafter adjustment of their relative intensities. The reproducing and'recording operations are similar to those employed when the waves are first recorded and then reproduced.

These and other features and objects of the present invention will be understood more clearly in-connection with the following deaccompanyin drawings, in which: ig. 1 is a graph showing the distribution of energy in the frequency spectrum of ordinai y speech.

figs. 2, 3, 5, 7, 8, 12, 14 and-17 are diagrams of different modifications of apparatus for recording Waves on a moving film.

Figs. 4, 6, 16 and 18 are fragmental side views of films bearing records produced in the apparatus of Figs. 3, 5, 14 and 17 respectively.

Figs. 9, 10, 13 and 15 are diagrams of different modifications of apparatus for reproducing waves from a film.

Fig. 11 is a graph showing the relation of inverted speech frequencies to the uninverted frequencies.

Fig. 19 is a diagram of apparatus for producing a secondary record from a primary record.

Referring to Fig. 1, the curve 1 was obtained from a study of the energy distribution of sound in normal speech. The abscissae of the curve represent wave frequencies in speech and the ordinates represent the energies of the respective waves. It will be seen that there are two fairly clearly defined frequency ranges in curve 1. The lower range embraces all the fundamental frequencies of normal s eech and the upper range embraces all the requencies necessary for clear reproduction of speech. It will also be noted that a very large proportion of the total energy lies in the lower frequency range, below 1000 cycles, the waves in the higher frequency range being relatively weak.

In Fig. 2 the apparatus is arranged to makeuse of the relationship shown in Fig. 1

between the energy and frequency of waves to be recorded. lectrical waves from the speech input 2 are separated into a high frequency range and a low frequency range by means of a high pass filter 3 and a low pass filter 4, respectively, of any well known suitable type. The filter 3 efliciently transmits waves having a frequency in excess of about 1000 cycles per second and prevents the transmission of appreciable current of lower frequency, while the filter 4 efiiciently transmits waves having a frequency below 1000 cycles per second and prevents the transmission of a preciable current of higher frequency. f desired filters 3 and 4 may be designed 'to separate frequencies above and below some critical frequency other than 1000 cycles. Thewavcs of high frequency are transmitted to the amplifier 5 conventionally shown as being of the spare current type but which may be of any well known type capable of amplifying waves without substantial distortion. The output circuit 6 of the amplifier is connected to the light control element 7 of any well known construction capable of transmitting a beam of light 8, the rays of which either vary in intensity or in direction in accordance with the electric potentials impressed upon the element.

The output circuit 9 of filter 4 1s connected in parallel with the amplifier output circuit 6. High frequency waves from oncuit 6 and low frequency waves from circuit 9 are thus transmitted together to the light control element? to'producc light variations corresponding to the impressed waves. The light variations ar transmitted through a narrow slit 10 Figs. 2 and l in an opaque screen 11 in front of the moving picture film, or film of other type 12, which is longitudinally moved transversely to the beam of light 8 by rotating spur gears 13 meshing with perforations 14 in the film or similar means. The speech input 2 in Fig. 2, and

in any of the figures, may b a source of electric waves corresponding to speech, music and other sounds or waves having componentsrelatively remote from each other in the frequency scale. y

In operating the apparatus shown in Fig. 2, high frequency waves from the source 2 are transmitted separately from the low frequency waves, the high frequency waves being transmitted through filter 3 and amplified by amplifier 5 .and transmitted in amplified form to the light control element 7. The low fre uency waves are transmitted through filter 4 and circuit 9 to element 7 without amplification. The amplified high frequency waves and the .unamplified low frequency waves together produce variations in the light rays 8 corresponding to the waves from source 2 and produce a photographic record on film 12.

lVhen the light variations consist of variations in the intensity of a beam of light of constant width, the record produced consists of a series of variations in the transparency of the film corresponding to th intensity variations of the light. When the light variations consist of variations in the direction of a beam of light of constant intensity, variable portions'of the beam are screened from the film by screen 11, and the record consists of a band of uniform transparency or opacity, varying in width in accordance with the variations of light direction.

The amplification of the high frequency waves by amplifier5 is adjusted to any desired value such that the high frequency waves are recorded with the proper intensity in relation to the low frequency waves. Preferably the amplification is adjusted to such a value that the high frequency waves may be reproduced from the record with the same amplitude in relation to the reproduced low frequency waves as that existing between the high frequency and the low frequency waves transmitted from source 2. After the film has been exposed to the light variations, the record is photographically developed, so that it becomes permanent and ready for reproduction.

In Fig. 3, the source 2 transmits waves selectively through filters 3 and 4. The high frequency waves transmitted through filter 3 operate light control element 15, while the low frequency waves transmitted from filter 4 operate the light control element 16 so that separate beams of light, corresponding respectively to the high frequency waves and the low frequency waves, are transmitted to the film 12 through slits 10 and 17 respectively, producing the records 18 and 19 parallel to each other on film 12. The dotted lines, encircling slits 10 and 17, Fig. 4 represent the edges of the areas illuminated by light from elements 15 and 16, Fig. 3. The partition 20 screens from record 19 the light intended for record 18 and vice versa. By separately transmitting light variations corresponding respectivcly to the high frequency waves and the low frequency waves a better and more sharply contrasted record of the high frequency waves isobtained than when the high frequency and low fre uency waves are recorded together as in ig. 2, and the obliterating effect of the low frequency record on the high frequency record is avoided. Records 18 and 19 are preferably disposed as shown adjacent the margin of film 12 so that the center space on the film may be utilized for moving pictures synchronized with the recorded sounds, for example, speechv or music. Filters 3 and 4 in Fig. 3 are of the same design as those in Fig. 2.

In Fig. 5, the light control element 21 produces variations in the direction of the beam oflight in accordance with the high frequency wavestransmitted from sources 2 through the high pass filter 3, while the light 'control element 22 produces Variations in the intensity of light corresponding to low frequency waves from the source 2 transmitted'through low pass filter 4. The light variations from elements 21 and 22 are separately recorded on the film 12, and are preferably so adjusted that the high frequency record 23 is of greater width than the low frequency record 24, as shown in Fig. 6. By allotting a larger space'for the high frequency record, the high frequency waves may be more acqu-ately reproduced than if restricted to as small an area as the low frequency record. By re cording the low frequency waves as variations in the transparency of the film it is possible to restrict the width of the low frequency waves to such a narrow strip on the film that the total width of the two records is less than that of the single record produced by the apparatus of Fig. 2. At the same time the quality of the reproduced waves is higher than that obtainable when the waves are recorded by the apparatus of Fig. 2.

In Fig. 7, waves from the source 2 are transmitted to amplifiers 25 and 26. Amplified waves from the output circuit of amplifier 25 are transmitted to the light control element 27, which in turn produces variations of light in accordance with the waves from source 2, these variations being recorded on film 12. Owing to limitations in the wave transmission characteristics of photoelectric cell used in reproduction when subjected to light variations from a narrow tively reproduced.

In order to reproduce a record corresponding to waves having a frequency in excess of 2500 cycles, amplified waves fromthe output circuit of amplier 26 are transmitted to the speech inverter 28, wherein the frequency spectrum of the waves from source 2 is inverted, as by a modulating operation with the elimination of unmodulated components of carrier wave and modulating wave freuency. When speech is to be recorded, t e carrier wave frequency is preferably of the order of 4500 cycles, that is, of the order of the highest speech frequencies. A specific form of inverter circuit is disclosed in connection with Fig. 12. The inverted or modulated waves from inverter 28 are transmitted to light control element 29 which produces light variations corresponding to the waves from source 2 but having frequencies arranged'in reverse order from that in which they occur in the output circuit of source 2. These light variations are recorded beside the record of light variations from element 27. Element 29, together with the associated apparatus is similar to element 27 in functioning as a frequency selective element which permits only those frequencies below, say approximately 2500 cycles, to be effectively recorded. However, since the waves of inverted frequency, below 2500 cycles, corresponds to original frequencies above 2000 cycles, it will be seen that the resulting record of the inverted waves is really a record of original waves in the high frequency range above 2000 cycles, the record of the uninvertedwaves together with the record of the original uninverted waves constituting a complete record of the waves from source 2.

Fig. 8 shows the source'2, ampllfiers 25 and 26, speech inverter 28, and light control elements 27 and 29, as in Fig. 7. Light rays from element 27 are transmitted through the color filter 30,. which selectively transmits lightof one color to the exclusion of light of'other colors, the transmitted light being recorded on the film 31. Light from element 29 is transmitted through the color filter 32. which selectively transmits light of a different color fr o n that of filter 30 to the exclusion of other...colors, the transmitted light being directed through the same slit 10 as the light transmitted through filter 30. Film 31 is designed to produce colored records corresponding respectively to the colors of the light transmitted to the film. This may be any of the well-known types of films sensitive to colored records, such as for example, that described on page 268 of Behind the motion picture screen by A. C. Lescarboura, Scientific American Publishing Company. For example, if blue li ht be transmitted from element 30 and ye? transmitted from element 32, film 31 is designed to respond selectively to these colors and produce corresponding records in blue and yellow colors superposed on each other.

by the method described in connection with Fig. 2, only a single strip, or record 18, of exposed area on the film, is utilized in the reproduction of waves from the record. Film 12 is longitudinally moved by rotating spur gears 13, as in Fig. 2, the record 18, which for the present may be assumed to have been produced by the apparatus shown In Fig. 2, is illuminated on one side by light from the incandescent electric lamp, or other source of light 34. Lens 35 concentrates the light on the film through a slit 10, corresponding to that in Fig. 2, registering with record 18. As the film moves transversely to the light from source 34, light is variably transmitted to photo-electric cell 36, these variations in light corresponding to varia tions in the transparency of the record 18.

Photo-electric cell 36, which may be of any well known suitable design capable of producing electric waves in accordance with variations of the light impressed on the cell, transmits the waves to amplifier 37, the am plification of the reproduced waves being adjusted by means of potentiometer 38, or other suitable gain control apparatus. Amplified waves from the output of amplifier 37 may be still further amplified to any desired extent by other am lifiers such as amplifier 38, the output of which is connected to the wave responsive device 39, of any suitable form, conventionally represented in the drawing as a loud s eaking telephone receiver. Com sidering ig. 2 in connection with upper path of Fig. 9, it will. be noted that the relative amplitudes of waves in the'high frequency range and the low frequency range may be adjusted relativel to each other by controlling the amplification in amplifier 5, so that the distortion of waves in the course of transmission from source 2 to device 39 is substantially compensated, and the sound reproduced by device 39 conforms closely to the sound or other energy giving rise to the waves from source 2.

low light be 7 When reproducing waves recorded by apparatus shown in Fig. 3 wherein two records are arrai'iged side by side on thefilm, the separate records 18 and 19 may be reproduced by separate photo-electric cells or b a single cell. When separate cells are use high frequency waves are reproduced from record 18 as already described, while low frequency waves are reproduced from record 19 by photo-electric cell 40 in a manner similar to that described in connection 'with cell 36, the source of light 41 transmitting light through record 19 to produce variations in the excitation of cell 40 in accordance with the variations of transparency in the record. Waves from cell 40 are transmitted through amplifiers 42 and 43. The speech inverter 44 is omitted when re roducing waves recorded by the apparatus 0 -Fig. 3. Amplified waves from devices 38 and 43 are transmitted together to the receiver 39, which reproduces the waves in the form of sound corresponding tothe original sound from source 2, Fig. 3.

By means of the gain control apparatus 38, the relative amplitudes of waves in the high frequency and low frequency ranges, respectively, are adjusted to compensate for distortion produced in the apparatus between source 2 and receiver 39. If desired, cell 40 and its connections to receiver 39 may be omitted, cell 36 being so disposed as to respond to variations of the light transmitted through both records 18 and 19, thus affording a simpler form of reproducing apparatus. If desired, one of the sources 34 or 41 may be omitted and light from the other source directed through both records 18 and19, as shown in Fig. 19.

lVaves recorded by the apparatus shown in Fig.5 may be reproduced by the appay ratus of Fig. 9, in the manner just described in connection with Fig. 3. It will be noted that record 23 consists of an exposed strip of constant transparency or opacity and of varying width, whereas record 24consists of a strip of constant width and of varying transparency. The beam of light transmitted through record 23 accordingly varies in width rather than in intensity but produces a similar excitation of photo-electric cell 36 as that produced by the li ht of varying intensity transmitted throng 1 record 24. Owing to the greater width of record 23 and to the method by which the waves are recorded, the reproduced high frequency waves are of better quality than if recorded by the method used in producing record 24. At the same time the method used in producing record 24 saves space on the film without detriment to the quality of the reproduced low frequency waves.

\Vhen the record is produced by the apparatus shown in Fig. 7 the waves may be reproduced by the apparatus shown in Fig. 9,

the records 18 and 19 corresponding respectively to the record of the unmodulated waves and the record of the inverted or m'odulated waves. Record 18 is reproduced in the manner already described, the reproduced waves being transmitted to receiver 39. Inverted or modulated waves reproduced from record 19, are transmitted from cell 40 to amplifier 42 and speech inverter 44, which may be of any suitable type, such for example, as speech inverter 28, Fig. 7. Inverter 44 inverts or demodulatcs the inverted or modulated waves and restores them to the original frequencies of the waves from source 2 to which they correspond. The demodulated waves are amplified by amplifier 43 and transmitted to receiver 39 where they sugplement the action of waves from amph er 38. Inasmuch as the entire range of wave frequencies from source 2, Fig. 7, are recorded and reproduced in Fig. 9, at relatively low frequencies as compared to the highest frequencies of the original waves to be recorded and of the final reproduced waves, the waves transmitted to receiver 39 are comparatively free from distortion such as would be encountered if the waves in the high frequency range were transmitted without frequency change and without inversion. Other features of the method of and apparatus. for recording and reproducing waves by modulation are described in connection with Figs. 11 and 12.

Fig. ,10 shows reproducing apparatus for use in conjunction with the recording apparatus of Fig. 8. Source 34 transmits light through the superposed colored records on film 31. Color filter 45 selectively transmits one color to the exclusion of other colors, and, in the example cited, where blue and ellow records are superposed, transmits only blue light which excites photo-electric cell 36 corresponding to cell 36, Fig. 9. Color filter 46 selectively transmits colored light from the other record, exclusive of all 1 other colors, and, in the example cited, transmits yellow light to photo-electric cell 40, corresponding to cell 40, Fig. 9. \Vaves from cells 36 and 40 are transmitted to receiver 39 in the manner described in connection with Fig. 9, the inverter 44 inverting or demodulating the waves from cell 40 before transmission to receiver 39. Except for recording and reproducing the records by color selection, the operation of Fig. 8 in connection with Fig. 10 is similar to that of Fig. 7 in connection with Fig. 9. The principles of recording and reproducing in colors, as described, may be applied to Figs. 3 and 5 in connection with Fig. 10, similarly to the manner in which they have been applied to Figs. 7 and 9.

Fig. 11 shows diagrammatically the frequency relationship between the original waves from source 2, and the inverted waves -the frequency scale.

of most importance, produced by inversion of the frequency spectrum of the original waves. The abscissee indicate frequencies. The range extending from substantially zero to 2500 cycles is readily recordable and reproducible by well known methods. The range from 2500 cycles to 4000 cycles, is important in determining the clearness of articulation of s eech and the quality of music, but is of too igh frequency to be suitably recorded and reproduced by ordinary methods. By modulating a carrier wave of 4500 cycles in accordance with speech waves, the waves of inverted frequency corresponding to the range extending from 2500 cycles to 4000 cycles, are reduced in frequency, and at the same time the frequency spectrum of the original waves from 2500 to 4000 cycles is inverted, so that a Wave having an original frequency of 2500 cycles becomes a Wave of 2000 cycles upon inversion, and an original wave of 4000 cycles frequency becomes a wave of 500 cycles frequency. The heavy dashed horizontal line 50 represents the extent and location of the inverted waves in The oblique dashed lines extend from components before inversion to the corresponding components after inversion, showing graphically the inverted relationship.

Fig. 12 shows a well known arrangement for inverting j or modulating sound Waves, the modulating apparatus being of the type disclosed in detail in U. S. Patent to R. V. Hartley 1,419,562 of June 13, 1922. The telephone transmitter 51 produces electric waves corresponding to the sound impressed thereon. These waves, together with carrier Waves from the local source 52, preferably of 4500 cycles when speech is to be recorded, are transmitted to the balanced modulating tubes 53. As described in the patent cited, tubes 53 are so associated, that only waves of modulated frequencyappear in output circuit 54, the unmodulated waves of modulating frequency from source 51' and of carrier fr uency from source 52, being suppressed 5310111) transmission through circuit 54. Modulated waves from circuit 54 are transmitted to the light control element 55 of similar construction to that of light control element 7, Fig. 2, which transmits light'variations to film 12 whereon a corresponding record is produced. Owing to the transmission characteristics of the recording and reproducing ap aratus, the lower frequencies are more satis actorily recorded on film 12 than the higher frequencies. However, by inversion before recording and reinversion upon re roduction the higher frequencies are satis actorily reproduced. The record on the film may be affected by the low frequencies in the up er side band of the modulated waves. T e presence on the record of the low frequencies in the upper side band is not I objectionable since demodulation of the up- 1 per side band produces the samefrequencies as demodulation of the lower side band.

It is obvious that the modulating or in-' verting apparatus of Fig. 12 may be utilized in place of the speech inverter shown in any of the preceding Figs. 7, 8, 9 and 10.

Fig. 13 shows apparatus for reproducing speec or sounds corresponding to those actuating transmitter 51 and recordedon record 12, Fig. 12. Light from source 34 is concentrated on the film and transmitted therethrough to photoelectric cell 56, from which waves are transmitted to the coil 57 which magnetically vibrates the elastically restorable conducting member 58 between the microphonic contacts 59. Contacts 59 are connected respectively to-opposite ends of the primary winding of transformer 60, the mid-point of which is connected throu h transformer winding 61 to member 58. T e local source of carrier waves 62, ofthe same frequency as waves from source 52, is coupled to winding 61. Coil 57 together with elements 57 and 62, inclusive, constitute a balanced demodulator of well known form in which, waves impressed on coil 57 are demodulated, the demodulated waves being transmitted to the secondary winding of l2l2tllSf0l'll'lQI 60. Filter 63 of well known construction is designed to suppress the transmission of waves from source 62 and to efficiently transmit demodulated waves of other frequencies corresponding to waves from source 51. Demodulated waves are we transmitted to receiver 39, which produces sound corresponding to that acting on transmitter 51, Fig. 12 v Fig. 14 shows recording apparatus particularly adapted for high quality work, and 105 intended especially for use in recording music and sounds of diflerent origin and kind. The sounds may consist of vocal, or instrumental sounds, or music, with a piano, orchestra, or other accompaniment. The plu- 110 'rality of sources 65, 66, 67 and 68. each adapted to pick up music from an individual singer, or instrument, or group of sound sources of similar kind, are arranged to produce separate records on the film 69. When 115 vocal or instrumental music isto be recorded with an accompaniment, source 65'may be made responsive to the rinci al .music, vo-

cal or instrumental, wit out t e accompaniment, and sources 66, 57, etc., being made responsive respectively to the different classes of sounds in the accompaniment. When an orchestral or concert selection is to be recorded, sound sources of similar character may be-grouped and arranged to produce waves in a single wave source 65 or 66. and so on. Source 65 is connected-to apparatus, such as shown connected to source 2 in Fig. 7 and produces a record corresponding to waves of unmodulated frequency in the lower frequency range of the original waves, and a se arate record of inverted waves correspon 'ng to original waves in the higher frequency range. Source 65, together with its connected apparatus, is therefore particularl adapted for recording vocal music or soun or instrumental sounds of corresponding range.

Sources 65, 66, 67 and 68 are similar to each other and non-microphonic-in character so as not to pick up sounds at a distance and each being connecting to apparatus for 1producing a separate record on film 69. Jach of these sources is connected to an amplifier 70, the amplification of which is adjusted by means of a potentiometer 71, individual to the amplifier. Before recording is begun the two pole switches 72 are thrown to the lower position connecting the amplifiers to the telephone receiver 7 3, by means of which the relative intensities of waves from the different sources may be observed, and proper adjustment of potentiometers 71 made, so that the waves from the separate sources will be recorded with the proper relative intensities, or, in other words, so that waves may be reproduced from the record in a well balanced relationship. Switches 72 are then placed in their upper positions establishing connection between amplifiers and light control elements 74, which transmit light producing separate records on film 69.

The width of the separate records is preferably adjusted, for reasons already given,

= so that the waves of higher frequency are recorded as a wider strip than the records of waves of lower frequency; for example in the case of film 69, Figs. 14 and 16, it is assumed that sources 66, 67 and 68 respond to waves of relatively higher frequency. Records 75 corresponding to waves from source 65 are records of low frequency waves, it being recalled that the high frequency waves from source 65 are reduced in fre uency by inversion and recorded in inverte form as waves of low frequency. Records 76, corresponding to waves of relatively higher frequency from sources 66, 67 and 68, are wider than records 75.

Fig. 15 shows apparatus for reproducing waves from film 69, the film being shown in more detail in Fig. 16. In reproducing the waves from record 69, light from source 34 is transmited through the film and the long slit 97 in the opaque screen 98. Lenses 77 are positioned so that light from a single record is focused exclusively on a corresponding photo-electric cell 7 8, thus selectively concentrating the light from any given record on a correspondin photo-electric cell and excluding the light from any other record. The upper two photo-electric cells are connected to apparatus corresponding to that shown connected to cells 36 and 40, Fig. 9, with the exception that a common amplifier 79 is substituted for separate amplifiers 38 and 43, Fig. 9. Thelower three cells 78,

to the uppermost cell 78, Fig. 15, the waves from all of the cells being transmitted after amplification to a common input circuit 80 for receiver 39. The operation of the individual circuits connected to photo-electric cells 78 is similar to that already described in connection, with Fig. 9.

One advanta e of recording and reproducing sounds by t e apparatus of Figs. 14 and 15, results from the separate recording of different kinds of sounds, particularly the recording of the low frequencies separately from the high frequencies whereb the resulting record is free from the ob iterating effect of the low frequencies on the high frequencies. Another advantage is that larger light variations are obtainable than is possible when using a single light varying element for a wide range of frequencies, a further advantage being that a Well balanced record can be easily made. Potentiometers 71 afl'ord convenient means for adjusting the loudness of the sounds from any particular source without requiring moving of the sound transmitter. By providing in the output circuit of cells 78, Fig. 15, potentiometers such as potentiometer-s 38 shown in Fig. 9, the intensity of sounds in the dilferent frequency range and from the different sources may be adjusted after record 69 is made, to obtain the desired combined sound from receiver 39. If desired, a single photo-electric cell may be subjected to the light from the records of the unmodulated waves, the output of the cell being connected to receiver 39, as shown in the circuit connected to the uppermost photo-electric cell 78, Fig. 15, thus providing a simplerform of reproducing apparatus.

The cost of recording sound by the multiple record method, while apparently large, may, in many instances, be justified, or actually prove to be less than that involved in producing a single record from a single light control element, for the reason that. when a single record is made to represent a large number of sounds, and the record is found to be defective due to lack of balance between the different components of sound, it is necessary to bring the artists and operators to the studio a second time in order that the record may be remade. A multiple record made in accordance with the principles of the present invention avoids this difliculty in -Fig. 15, are connected to apparatus similar that the proper relationship between the' being responsive to a dilferent sound source.

In order to obtain very high quality of reproduction of the original sounds waves from sources 81, 82, etc., after suitable amplification, are recorded by different methods accordin to the frequencies of the waves to be recorded, each method being chosen in view of its particular effectiveness for recording the particular range of frequencies concerned. The method of operation is similar to that described in connection with Figs. 5 and 6.

In the specific arrangement shown, sources 81 and 82 are assumed to transmit waves of relatively low frequency. These waves are efiiciently recorded by light control elements 83 and 84 respectively, which transmit to film 85, narrow beams of light of constant width, the intensities of which vary in accordance with the waves from the associated wave sources. The resulting records 86 and 87 are comparatively narrow. It is assumed that sources 83' and 84 transmit waves having higher frequency components than those from sources 81 and 82. In order to obtain an eflicient record of the high frequenc waves, so that they may be reproduced wit proper intensity in relation to waves reproduced from records 86 and 87, the light control elements 88 and 89, connected respectively to sources 83 and 84, are of the type in which the direction of the beam of light varies in accordance with the waves impressed thereon. Records 90 and 91 produced by light variations from ,elements 88 and 89, therefore, consist of exposed strips of constant transparency or opacity, the widths of the strips varying respectively in accordance with waves from the associated sources 83 and 84'.

Fig. 18 shows the film 85, hearing the narrow records 86 and 87, consisting of exposed strips of varying transparency, and the exposed strips 90 and 91 of varying width. The opaque screen 78, having aslit 77 registering with all of the exposed strips, functions similarly to the corres onding parts in Fig. 16. Reproduction Q? waves from records 86, 87, 90 and 91 is accomplished by apparatus of the kind described in connection with Fig. 15.

Fig. 19 shows apparatus arranged to automatically produce a secondary or master record from a primary or preliminary rec- 0rd, or, in other words, to transfer one or more records from one film to another. The source of light 34 illuminates the film 12, transmitting light through the film and exciting the photo-electric cells 36 and 40 in the manner described in connection with Fig. 9.

Instead of connecting the output circuit of amplifiers 37 and 42 to a single responsive element 39, as shown in Fig. 9, separate light control elements 92 and 93 are connected res ectively to these amplifiers to respond to t e impressed waves and transmit light variations to film 94 and produce separate records 95 and 96 thereon, corresponding to records 18 and 19 on film 12. By varying the amplification of amplifier 37 with respect to that of amplifier 42, as described in connection with Fig. 9, waves in the two different ranges represented byrecords 18 and 19 ma be readjusted with respect to each other so t iat a better balance is obtained in records 95 and 96. In adjusting the amplification of amplifiers 37 and 42, use may be made of tion, film 12 may be run off with film 94,

whereby a revised record on film 94 is automatically produced.

It is to be understood that film '12, as originally recorded, is ordinarily in the form of a negative, while film 94 is also a negative. The film distributed to exhibitors, such as motion picture exhibitors, for use in speech, music or sound reproducing projecting machines at motion picture theaters, or elsewhere, would ordinarily be positive films made as prints from the negative films. Film 94 is used as a master record from which any number of positive records may be printed for distribution. The transfer apparatus, shown in Fig. 19, makes it possible to conveniently revise a record or a plurality of records obtained from a concert, or the rendering of a musical selection, particularly where, under the circumstances, it is either impossible or objectionable to repeat the original recording process. The method disclosed permits of balancing the volume of an accompaniment to a solo, or of one part of the orchestra to the remainder, and so on.

While specific methods and arrangements utilized in the transmission, recording and reproduction of sounds and other waves have been described, it is to be understood that these specific forms are susceptible to various other obvious groupings, associations and uses than those specifically mentioned. Novel features of the invention are set forth in the appended claims.

What is claimed is:

1. In apparatus for recording and reproducing waves corresponding to sound, means for transmitting waves corresponding to sound within a given frequency range and for separately transmitting waves corresponding to sound within another frequency range, means for recording the transmitted waves, and means for reproducing from the resulting record waves corresponding to the original sound.

2. In apparatus for recording and reproducing waves, a source of waves corresponding to sound, means for transmitting from said source waves corresponding to sound above a given frequency, separate means for transmitting'from said source waves corresponding to sound below said frequency,

means for recording saidtransmitted waves,-

and means for reproducing from the resulting record waves corresponding to the original sound.

3. In apparatus for recording and reproducing waves corresponding to sound having components remote from each other in the frequency scale, record receiving means, means for producing thereon a record of waves corresponding to said components, said record producing means including means for controlling the recording of waves corresponding to said components of high frequency separately from waves corresponding to said components of low frequency, and means for reproducing from the resulting record waves corresponding to said components.

4. The method of recording and reproducing waves corresponding to sound, which comprises transmitting waves corresponding to components of sound having a frequency above a given value, separately transmitting waves correspondin to sound components having a frequency below said value, recording said transmitted waves, and reproducing said waves from the resulting record.

5. The method of recording and reproducing waves corresponding to speech, which comprises controlling the transmission of said waves corresponding to speech frequencies of the order of one thousand cycles per second or higher, separately controlling the transmission of said waves corresponding to lower speech frequencies, recording the waves thus transmitted, and reproducing from the resulting record waves corresponding to said speech.

6. The method of recording a wave band within which waves in a given frequency range have relatively small energy as compared with waves outside said range, which comprises transmitting and amplifying the waves within said range, separately transmitting the waves outside said range, and recording the amplified waves and the waves outside said range.

7. The method of recording waves corresponding to speech, which comprises transmitting said waves corresponding to the components of speech having a frequency above a given value, separately transmitting said waves corresponding to components of speech having a frequency below said value, amplifying said waves corresponding to said higher frequency components, and recording the amplified waves and the transmitted waves corresponding to said low frequency components.

8. In sound recording apparatus, means for producing electric waves varying 1n accordance with the sound, a plurality of transmission circuits connected thereto,

means in one of said circuits for selectively transmitting waves within a given frequency range, means in another of said circuits for selectively transmitting waves within another frequency range, unitary means for receiving a record of said waves, and means for recording thereon the waves transmitted by said circuits.

9. In apparatus for recording waves corresponding to sound, means for receiving a record of said waves, and means for sepa rately recording thereon said waves corresponding respectively to sound components within a given frequency range and to components outside said range.

10. In apparatus for recording waves corresponding to sound, means for transmitting a wave corresponding to a sound of high frequency and for separately transmitting a wave corresponding to a sound of low frequency, means for receiving a record of said waves, and means for separately recording thereon the transmitted waves correspondin respectively to the high frequency sound an the low frequency sound.

11. In sound recordingapparatus, means for producing electric waves varying in accordance with the sound, a plurality of transmission circuits connected thereto, means in one of said circuits for selectively transmitting waves within a given frequency range, means in another of said circuits for selectively transmitting waves within another frequency range, unitary means for receiving a record of said waves, and means for separately recording thereon the waves tansmitted respectively by said separate circuits.

12. In wave transmitting apparatus, a source of waves of different frequencies, and means connected'to said source for variably transmitting light in accordance with said waves, said light transmitting means including means for separately controlling the light variations corresponding respectively to the high frequency waves and the low frequency waves.

13. In apparatus for recording waves corresponding to sound, means for transmitting said waves, means connected to said transmitting means for variably transmitting light in accordance with said waves, said light transmitting means including means for separately controlling the light variations corresponding respectively to the high frequency sounds and the low frequency sounds, and means for receiving a record of .said light variations.

I 5 spectively to sounds of different frequency.

ing said light variations.

16. The method of recording waves corresponding to sound, which comprises variably transmitting light in accordance with said waves, separately and differently controlling said light variations corresponding-respectively to sounds of high frequency and to sounds of low frequency, and photographically recording said light variations.

17. The method of recording on a strip of photographic film light variations corresponding to sound waves, which comprises progressively recording along a path on the strip variations of light corresponding to sounds of low frequency, and progressively recording along one side of the path variations of light corresponding to sounds of high frequency.

18. A sound record comprising a photographic film having a plurality of records, each of different color, corresponding re- 19. A sound record comprising a photographic film having a plurality of records superposed on each other, each of different color, corresponding respectively to sounds of different frequency. v

20. In apparatus for recording and reproducing waves of different frequencies, means for transmitting'said waves, means for receiving a record of said waves, means for producing on said record receiving means a record of said waves of low frequency, means for reducing the frequency of said waves of high frequency, means for producing on said record receiving means a record of said waves of reduced frequency, and means for producing from the resultin record waves corresponding to said originalwaves. a

21. In apparatus for recording waves of different frequencies, means for transmitting said waves, means for receiving a record corresponding to said waves, means for producing thereon a record of said waves of low frequency, means for reducing the frequency of said waves of high frequency, and means for producing on said record receiving means a record of said waves of reduced frequency.

22. In apparatus for producing a record of waves of different frequencies, means for transmitting said waves, means for receiving a record of said waves, means for producing on said record receiving means a record of said waves of low frequency, means for inverting and lowering the spectrum of said waves of high frequency, and means for producin on said record receiving means a recor of the inverted components.

23. The method of recording and reproducing sound, which comprises producing waves corresponding to the sound, modulating a carrier wave in accordance with said waves, producing a photographic record of the modulated components in the resulting waves, simultaneously producing a photographic record of the unmodulated first mentioned Waves, separating reproducing waves corresponding to said records, demodulating the resulting carrier waves, combining the demodulated waves with the reproduced unmodulated waves, and producing sound in accordance with the combined waves.

24. In sound reproducing apparatus, a plurality of sound records, separate means for simultaneously producingwaves corresponding respectively to portions of said separate records, means connected to one of said wave producing means for inverting the frequency spectrum of the waves produccd thereby, and means common to said inverting means and to said other wave producing means for producing a sound corresponding tothe resulting waves.

25. In sound reproducing apparatus, a film having a plurality of complementary records thereon, each of different color, means for illuminating said film with light of said colors, separate means, each for selectively transmitting a different one of said colors from said film, separate means associated with each said selective means for producing waves corresponding to variations in the light transmitted by said selective means when said film is longitudinally moved transversely to the light, and means controlled by the resulting waves for producing sound corresponding to said complementary records.

26. A method of recording and reproducing waves corresponding to sound on a recording means which efliciently records only waves below a certain frequency, which comprises producing a record on said means cor responding to said waves, inverting said waves to bring those above said limiting frequency into the region below said limit, separately recording said inverting waves and ing sound on a medium, which efliciently records only waves below a certain frequency range which comprises producin electrical waves corresponding to said soun transmitting said electrical waves to 'a recording means and recording said waves onsaid medium, separately transmitting said waves to a modulator, modulating said waves therein with a carrier wave to produce a modulated wave, free from unmodulated components, in which the waves outside said range are brought within the range, producing on said medium a record corresponding to said modulated wave and reproducing the original sound from the resulting record by producing electrical waves corresponding to directly recorded waves and to saidmodulated waves, demodulating said last waves and producing sound corresponding to said first waves and to said demodulated waves.

28. In an apparatus for recording sound on a recording medium only efiiciently sensitive to frequencies within a-certain ran 0, means for dlrectly recording on said me ium frequencies within said range, means for changing the fre uency spectrum of said sound to bring the requencles outside said range within said range, and separate means for recording said chan ed spectrum.

29. An apparatus for recor diflerent fre uencies on a recording medium only efficient y sensitive to frequencies below a certain limit, means for producing on said medium a record of said waves below said limit, amodulator for modulating said waves with a carrier wave of a frequency in the neighborhood of said limiting frequency to produce modulated waves free from unmoduIa-ted components and means for producing on said medium a record of said modulated waves.

In witness whereof, I hereunto subscribe my name this 19th da of June A. D., 1924.

CHARLE D. LINDRIDGE.-

mg waves of v 1,675,894.0harles D. Dindrid e,

- sponding to sound, means for transmitting from said DISOLAIMEFFL Montclair, N. J. METHOD AND APPARATUS FOR RECORDING AND REPRODUCING SOUND. Patent dated July 3, 1928. Disclaimer filed March 4, 1931, by the assignee, American Telephone and Telegraph Company.

Hereby enters this disclaimer to the said claims of said Letters Patent which are in the following words to wit: 4 1'. In apparatus for recording and reproducing Waves corresponding to sound, means for transmitting wav,es corresponding to sound wlthin a given frequency range quency range, means for recordlng the transmitted waves, and means for reproducing from the resulting record waves corresponding to the original sound. I

2. In apparatus for recording'and reproducing waves, a source of waves corresource waves corresponding to sound above a given frequency, separate means for transmitting from said source waves corresponding to mltted waves, and means for reproduclng from the resultmg record waves correspondmg to the origmal sound.

Waves corresponding to said components of high frequency separately from waves corresponding to said components of low frequency, and means for reproducing from the resulting record waves corresponding to said components.

:4. The method of recording and reproducing waves corresponding to sound waves corresponding to said speech.

6. The method of recording a wave band within which waves in a given frequency range have relatively small energy as compared wlth waves outside said range, which 9. In apparatus for recording Waves corresponding to sound, means for receiving a record of said Waves, and means for separately recording thereon said waves corresponding respectively to sound components Within a given frequency range and to components outside said range. I

10. In apparatus for recording waves corresponding to sound, means for transmitting a wave corresponding to a sound of high frequency and for separately transmitting a Wave corresponding to a sound of low frequency, means for receiving a record of said waves, and means for separately recording'thereon the transmitted waves corresponding respectively to the high frequency sound and the loW frequency sound.

11. In sound recording apparatus, means for producing electric waves varying in a plurality of transmission circuits connected thereto, means in one of said circuits for selectively quency range, means in another of said circuits for selectively transmitting Waves sound below said frequency, means for recording said transtransmitting waves within a given frewithin another frequency range, unitary means for receiving a record of said waves, and means for separately recording thereon [the waves transmitted respectively by said separate circuits. v

-12. In wave transmitting apparatus, a source of waves of different frequencies, and means connected to said source for variably transmitting light in accordance with said waves, said light transmitting 'means including means for separately controlling the light variations corresponding respectively to the high frequency waves and the low frequency waves.

13. In apparatus for recording waves corresponding to sound, means for transmitting said waves, means connected to said transmitting means for variably transmitting light in accordance with said waves, said light transmitting means including means for separately controlling the light variations corresponding respectively to the high frequency sounds and the low frequency sounds, and means for receiving a record of said light variations.

14. In apparatus for recording waves corresponding to sound, means for transmitting said waves, means connected to said transmitting means for variably transmitting light in accordance with said waves, said light transmitting means including means for separately controlling the light variations corresponding respectively to the high frequency sounds and the low frequency sounds, and a photographic film having a portion exposed to said light variations and arranged for longitudinal movement transversely to the incident light rays.

15.,The method of reeordlng waves corresponding to sound, which comprises variably transmitting light in accordance with said Waves, separately controlling said light variations corresponding.respectively to sounds of high frequency and to sounds of low frequency, and photo raphically recording said light variations.

"17. The method of recor ing on a strip of photogra h1c film light variations corresponding to sound waves, which comprises progressive y recording alon a pathon the strip variations of light corresponding to sounds of low frequency, and progressively recording along one side of the path variations of light corresponding to sounds of high frequency.

[Ofiicial Gazette M arch 24', 1931.] 

